Numerous attachment devices are generally known for operatively connecting turbomachinery rotor elements, such as rotors, to drive shafts. Keys, tapered polygon couplings, splines, and conical tapers are all rotor element attachment devices.
Threaded couplings can transmit high torque loads, and are easy to manufacture, but have an inherent disadvantage of being unidirectional. If torsional load is applied counter to the direction of thread pitch, the rotor will decouple from the shaft with resultant damage to the machine, and costly production losses. Numerous decoupling prevention devices have been applied to threaded couplings to overcome this problem, but they all increase manufacturing costs, and most do not have true bi-directional torque transmission capability in that torque carrying capability under reverse rotation conditions is less than under normal forward rotation conditions.
Turbo-machines often operate under a wide variety of torque loads. Due to component weight considerations, or process conditions, it is often desirable that turbomachinery incorporate rotors of especially soft or especially brittle materials. The ability to transmit torque through these materials without deformation due to stress loads often requires that an additional part, manufactured from alternate material, be fixedly inserted into the rotor hub for the purpose of transmitting torque levels from keyed, conically tapered, or splined connections, which would not otherwise be feasible. An alternative is to decrease the stress loads by increasing the mating surface areas through the use of a shaft of increased diameter. Both of these options are undesirable in that they increase both weight and cost of the machine.
Polygon tapers provide an alternative coupling method relative to keys, conical tapers, or splines in that they are capable of carrying high torque loads, through very soft or very brittle materials, without the need for costly hub inserts. They are superior to threaded connections in that they have true bi-directional torque carrying capability. A disadvantage of polygon tapers, such as shown in U.S. Pat. No. 5,482,437, which is incorporated by reference herein, is that they require special tooling to be manufactured, such as machines capable of grinding internal bores to tapered polygon shapes, that are unavailable in most repair facilities, resulting in the delays and expenses related to transporting parts to specialty manufacturing facilities for repair.
Therefore there is a need for an improved means for operatively connecting turbomachinery rotor elements, such as impellers, to drive shafts that would: be capable of bi-directional transmission of high torque loads between the drive shafts and the turbo-machinery rotors; be capable of transmitting high torque loads between the drive shafts and turbo-machinery rotors manufactured from soft or brittle materials; and be manufacturable or repairable using equipment and manufacturing practices available to most machine shops.